MIT scientists have used an ultrathin film of carbon nanotubes (CNTs) to produce aerospace-grade composites.
According to the team which includes MIT professor Brian Wardle, lead author and MIT postdoc Jeonyoon Lee, and Seth Kessler of Metis Design Corporation, the new method requires no warehouse-sized ovens and autoclaves, and could help speed up the manufacturing of airplanes and other large, high-performance composite structures, such as blades for wind turbines.
In 2015, Lee along with another member of Wardle’s lab, created a new method to make aerospace-grade composites without requiring an oven to fuse the materials together.
Instead of placing layers of material inside an oven to cure, the researchers essentially wrapped them in an ultrathin film of carbon nanotubes (CNTs).
When they applied an electric current to the film, the CNTs, like a nanoscale electric blanket, quickly generated heat, causing the materials within to cure and fuse together.
With this out-of-oven (OoO) technique, the team was able to produce composites as strong as the materials made in conventional airplane manufacturing ovens, using only 1 percent of the energy.
The researchers next looked for ways to make high-performance composites without the use of large, high-pressure autoclaves that generate high enough pressures to press materials together, squeezing out any voids, or air pockets, at their interface.
Part of Wardle’s work focuses on developing nanoporous networks – ultrathin films made from aligned, microscopic material such as CNTs, that can be engineered with exceptional properties, including color, strength, and electrical capacity.
The researchers proposed that if a thin film of CNTs were sandwiched between two materials, then, as the materials were heated and softened, the capillaries between the CNTs should have a surface energy and geometry such that they would draw the materials in toward each other, rather than leaving a void between them.
The MIT team tested their idea in the lab by growing films of vertically aligned CNTs using a technique they previously developed.
They then laid the films between layers of materials that are typically used in the autoclave-based manufacturing of primary aircraft structures.
Once this was done, they wrapped the layers in a second film of carbon nanotubes, which they applied an electric current to to heat it up.
It was observed that as the materials heated and softened in response, they were pulled into the capillaries of the intermediate CNT film.
According to the scientists, the resulting composite lacked voids and is similar to aerospace-grade composites that are produced in an autoclave.
The team is next planning to scale up the pressure-generating CNT film; they have so far managed to work only with samples measuring several centimeters wide.
Image and content: Melanie Gonick/MIT